A geological perspective on calcareous nannoplankton evolution : biotic response to global change and environmental perturbations?
Abstract
Data di Pubblicazione:
2008
Citazione:
A geological perspective on calcareous nannoplankton evolution : biotic response to global change and environmental perturbations? / E. Erba, C. Bottini, C.E. Casellato, B. De Bernardi, D. Tiraboschi - In: Abstract Volume 6. Swiss Geoscience Meeting[s.l] : null, 2008. - pp. 331-332 (( convegno Swiss Geoscience Meeting tenutosi a Lugano nel 2008.
Abstract:
Recent environmental changes and climate instabilities pose urgent questions regarding biota ability to keep pace with
concurrent excess CO2, global warming and ocean acidification. Major concerns are addressed to the possibility of near future
extinctions causing a biodiversity loss and revealing a biota failure in sustaining rapid and progressive environmental
changes accelerated by anthropogenic impacts. However, the findings of new organisms in various ecosystems raise the
possibility that global change might stimulate biota speciation and/or innovation: novel life forms might represent temporary
adaptation to environmental stress or might be real new species evolved in response to global change.
The ocean, the oldest and largest ecosystem on Earth, best recorded global changes in climate and oceanic physical, chemical
and trophic parameters. Within the oceanic biosphere, calcareous phytoplankton plays a special role as: (1) is common
and widespread and consists of cosmopolitan and endemic taxa; (2) has a 220 My-long evolutionary history; (3) is one the
most effective calcite producers of the planet since the Jurassic; (4) is relevant for both the inorganic and organic carbon
cycle; (5) is extremely sensitive to environmental variations; (6) may directs climate change by altering albedo and absorption/
emission of atm-CO2 at large scale.
The Phanerozic geological record of global change unambiguously indicates that the Earth system already experienced
conditions of (super)greenhouse and (super)icehouse. Diversity pulses of calcareous nannoplankton are grossly coeval with
major events such as climate and sea-level changes, large magmatic episodes and variations in ocean structure and composition,
suggesting that evolutionary patterns are intimately linked to environmental modifications.
Our study aims at reconstruction of both tempo and mode of nannoplankton evolution and the causal/casual role of environmental
pressure. We explored time-intervals of (1) evolutionary acceleration in absence of coeval environmental change,
during a period of presumed climatic stability (Tithonian, latest Jurassic), and (2) global change marked by calcareous phytoplankton
adaptation/evolution (Early Aptian Oceanic Anoxic Event 1a; PETM). For each case history calcareous nannofossils
have been investigated in sections from different oceans in order to discriminate among local, regional or global causes,
and to verify possible diachroneity in calcareous phytoplankton evolution and/or in response to global changes. Calcareous
nannofossil species richness, first and last occurrences and abundance (relative and absolute) have been achieved.
Morphometric analyses of selected taxa have been performed to separate malformation, under-calcification, over-calcification,
and real ultrastructure changes.
Three speciation models were proposed: phyletic gradualism, punctuated equilibrium and punctuated gradualism. Phyletic
gradualism holds that new species arise from slow and steady transformation of populations providing gradational fossil
series linking separate phylogenetic species. Punctuated equilibrium explains the appearance of new species by rapid speciation
occurring in small peripheral isolated populations, followed by migration to other areas where the fossil sequence
usually shows a series of sharp morphological breaks. Punctuated gradualism implies long-lasting evolutionary stasis interrupted
by rapid, gradual phyletic transformation without lineage splitting.
The Jurassic-Paleogene case-histories investigated provide examples of all evolutionary patterns in calcareous nannoplankton.
Preliminary results suggest: (1) potentially different speciation styles of coccoliths versus nannoliths; (2) that punctuated
graduali
Tipologia IRIS:
03 - Contributo in volume
Elenco autori:
E. Erba, C. Bottini, C.E. Casellato, B. De Bernardi, D. Tiraboschi
Link alla scheda completa:
Titolo del libro:
Abstract Volume 6. Swiss Geoscience Meeting